Remedial technique for maintaining well casing

ABSTRACT

A method for repairing a leak in a wellbore includes determining a location of the leak in the wellbore, lowering a casing drilling tool to approximately the location of the leak, drilling a hole in a casing lining the wellbore, pumping a sealing fluid into the hole drilled in the casing, and installing a plug in the hold in the casing.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 61/678,289, filed on Aug. 1, 2012, and entitled “Remedial Technique for Maintaining Well Casing Integrity and Inner Diameter,” which is incorporated by reference.

BACKGROUND

For wells produced using a thermal heavy oil production method, in particular Steam Assisted Gravity Drainage (SAGD) and Cyclic Steam Stimulation (CSS), there is sometimes a need to perform remedial work if the steam has broken through the cement barrier and is seeping to the surface.

Prior art remedial methodologies typically use of a combination of the ultrasonic imaging tool (USIT), Isolation Scanner cement evaluation service (both available from Schlumberger Technology Corporation of Sugar Land, Tex., USA), and cement bond logs to identify the source of the leak. Once the source of the leak is identified, the next step is typically to perforate the well where the leak has been identified, and squeeze cement into the perforations followed by the insertion of a liner. On rare occasions a casing patch will be used. In both cases, the remedial methods result in a reduction of effective casing inner diameter (ID).

SUMMARY

In one aspect, this disclosure relates to a method for repairing a leak in a wellbore that includes determining a location of the leak in the wellbore, lowering a casing drilling tool to approximately the location of the leak, drilling a hole in a casing lining the wellbore, pumping a sealing fluid into the hole drilled in the casing, and installing a plug in the hold in the casing.

In another aspect, this disclosure relates to a tool for repairing leaks in casing that includes a drill for boring through the casing, a seal for sealing around a hole in the casing, and a supply of sealing fluid.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows an example casing drilling tool positioned in a wellbore.

FIG. 2 shows an example of a tool as it drills a hole in the casing.

FIG. 3 shows an example of pumping a sealing fluid into the hole drilled into the casing.

FIG. 4 shows another example of pumping a sealing fluid into the hole drilled into the casing.

FIG. 5 shows an example of installing a plug in the hole.

FIG. 6 shows blown up view of a plug installed within a hole in the casing.

FIG. 7 shows an example of a method for sealing a leak in a wellbore.

DETAILED DESCRIPTION

A method for performing remedial work may include using a cased hole drilling type tool, such as the Cased Hole Dynamics Tester (CHDT™) available from Schlumberger Technology Corporation, to drill a hole in the casing in the area identified as the source of the leak, inject sealing fluid, and plug the hole, leaving a full diameter casing intact with full metallic pipe integrity. A cased hole drilling tool is described in U.S. Pat. Nos. 7,999,542; 5,779,085; 5,746,279; and 5,687,806, each of which is incorporated by reference.

A cased hole drilling type tool may be used to drill a hole in the casing in the area identified as the source of the leak. The tool may then inject a sealing fluid (e.g., cement) and plug the hole in the casing leaving the casing ID substantially intact.

To place the tool in the exact area that has been identified as the source of the steam leak, a gyroscope may be run downhole both during the leak identification phase and before the drilling phase.

In one example, the tool may include a packer that seals against the casing. Once a seal has been established the tool's drill bit drills a hole through the casing, cement, and formation.

The sealant injection phase may be performed using a pump module within the tool. The pump module is used to pump the fluid from a storage tank within the tool to the area behind the casing. The storage can be either sample chambers stacked to carry sufficient sealant volume. In another example, coiled tubing may be used to continuously delivering the sealant from the surface to the tool's flowline. This second method has the benefit of removing the sealant volume limitation that exists if the sealant is carried downhole using sample chambers.

Next, a plug may be installed in the hole drilled by the casing drilling tool. A mechanical expansion plug able to sustain bi-directional pressure differentials may be used. In one example, the mechanical plug material is selected such that the expansion rate of that material is the same or greater than the casing so that the severe temperature cycles characteristic of thermal production methods do not cause the plug/casing seal to be broken.

FIG. 1 shows an example cased hole drilling tool 20 that is positioned in a wellbore. In this example, the tool 20 is suspended in wellbore by a wireline 15. The tool 20 has a ring packer 22 and two anchors 24. The wellbore is lined with a casing 14 that is cemented into the wellbore with cement 12. The tool 20 is located in a region 10 where a leak has been identified.

The packer 22 may be urged against the casing to create a seal inside of which a hole may be drilled and through which sealing fluid may be pumped. This is just one example of how to make an effective seal. Other methods are known in the art, such as using double annular packers to create an isolated annular volume within the borehole. The tool 20 in the example of FIG. 1 also includes two anchors 24, which may be used to brace the tool during drilling and other procedures.

It is noted that FIG. 1, and the following figures, show a vertical wellbore arrangement. This is for ease illustration. Many SAGD and CSS wellbores are non-vertical, and even horizontal, in the locations were steam leaks commonly develop. The method described in this disclosure could be used for any leak from behind the casing, but one common leak is steam in SAGD, CSS, and other well heating applications. Thus, although shown vertically, a well needing repair could be at any orientation, including horizontal.

FIG. 2 shows an example of a tool 20 as it drills a hole in the casing 14. The packer 22 is urged against the inner wall of the casing 14 to create a seal. In the example of FIG. 2, a drill bit 33 is located at the end of a flexible shaft 31. The drill bit 33 drills a hole 39 through the casing 14 and into the cement 12 behind the casing 14. The hole 39 allows access to the cement 12 behind the casing 14 in the area 10 of the leak. In the example in FIG. 2, the anchors 24 are used to brace the tool 20 during the drilling process.

FIG. 3 shows an example of pumping a sealing fluid into the hole 39 drilled into the casing 14. The drill bit 33 and the flexible shaft 31 have been removed from the hole 39 and are retracted within the tool 20. A flowline 35 is then engaged within the tool so that fluid can flow out of the tool and into the hole 39. In FIG. 3, a pump 37 is shown which pumps the fluid from a storage area (not shown), through the flowline 35, and into the hole 39. The storage area may be sample collection tanks, as are known in the art, or another type of tank or container for holding the sealing fluid.

In one example, the sealing fluid is cement. Cement can be used to reinforce the cement 12 that is already in place behind the casing 14. Other sealing fluids may be used.

FIG. 4 shows another example of pumping a sealing fluid into the hole 39 drilled into the casing 14. In the example in FIG. 4, the tool 20 is run in the hole on a coiled tubing 45. Once the tool 20 is ready to pump sealing fluid, the sealing fluid may be pumped from the surface to the tool 20 through the coiled tubing 45. The coiled tubing 45 is connected to a flowline 41 within the tool. A valve 43 may be used to regulate the flow. Alternatively, a pump may be used within the tool 20 to regulate the flow of the sealing fluid to the hole 39 in the casing 14. As with the example in FIG. 3, the example in FIG. 4 shows the drill bit 33 and flexible shaft 31 disengaged from the drilling position. The packer 22 shown in the example in FIG. 4 is pressed against the casing 14 to form a seal so that the sealing fluid is forced to flow into the hole 39 drilled into the casing 14.

FIG. 5 shows an example of installing a plug 55 in the hole 39 once the leak has been repaired. The tool 20 is in the same position as in FIGS. 1-4, with the packer 22 urged against the casing 14 to create a seal. The anchors 24 are used to stabilize the tool against the opposite side of the casing 14.

In the example in FIG. 5, a piston within the tool 20 presses a plug 55 into the hole 39 in the casing 14. Pistons and other actuators for performing this task are well known in the art. The plug 55 is pushed from within the tool 20 into the hole 39 in the casing 14. In FIG. 5, the plug 55 is shown installed within the hole 39.

FIG. 6 shows blown up view of a plug 55 installed within a hole in the casing 14. In one example, the plug is able to sustain bidirectional pressure differentials. In another example, the plug material is selected so that the expansion rate of the plug 55 is the same or greater than that of the casing 14. This way in sever temperature cycles, the plug 55 will remain firm within the hole in the casing 14.

FIG. 7 shows an example of a method for repairing a leak in a wellbore. The method first includes determining the location of the leak, at step 61. This may include performing the logging activities to find the location of any potential leak. I may also include learning of the location of a leak based on the results of logging operations performed by others. It may be possible to determine the location of a leak without logging operations, if the leak location is otherwise known.

The method shown in FIG. 7 next may include lowering a cased hole drilling tool into a wellbore, at step 62. Such a tool may be lowered on a wireline, a coiled tubing, a slickline, or any other method to lower a tool into a well. For example, many SAGD wells are horizontal in the area where steam may leak through. In some horizontal wells, a tool such as a cased hole drilling tool may be moved along the well by a tractor. Coiled tubing or drill pipe may also work in such a situation, as well as any other conveyance known in the art. FIG. 1 shows an example of a tool 20 that has been lowered into a well.

The method shown in FIG. 7 may include drilling a hole in the casing, at step 63. An example of a drilling procedure is shown in FIG. 3. A drill bit is extended from the tool and used to bore a hole into the casing. Thereafter, the drill bit may be retracted into the tool so other operations may be performed.

The method shown in FIG. 7 may include pumping sealing fluid into the hole in the casing, at step 64. Examples of such operations are shown in FIGS. 4 and 5. The sealing fluid is pumped through the hole so that it can fill in any holes or gaps in the cement behind the casing. In one example, the sealing fluid is cement.

The method may include installing a plug in the hole, at step 65. The plug is inserted so that the sealing fluid stays behind the casing and to prevent wellbore fluid from leaking behind the casing during further operations.

Although only a few example examples have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example examples without materially departing from this invention. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims. Moreover, examples disclosed herein may be practiced in the absence of any element which is not specifically disclosed. 

We claim:
 1. A method for reparing a leak in a wellbore, comprising: determining a location of the leak in the wellbore; lowering a casing drilling tool to approximately the location of the leak; drilling a hole in a casing lining the wellbore; pumping a sealing fluid into the hole drilled in the casing; and installing a plug in the hold in the casing.
 2. The method of claim 1, wherein the sealing fluid comprises cement.
 3. The method of claim 1, wherein the plug is a mechanical expansion plug able to sustain bi-directional pressure differentials.
 4. The method of claim 1, further comprising: setting a packer in the casing drilling tool before drilling the hole; and wherein pumping the sealing fluid into the hole drilled in the casing comprises pumping cement from a chamber within the casing drilling tool.
 5. The method of claim 1, wherein pumping the sealing fluid into the hole drilled in the casing comprises pumping a cement from the surface through coiled tubing coupled to the cased hole drilling tool.
 6. The method of claim 1, wherein the plug is made of a material selected such that an expansion rate of the material is the same or greater than an expansion rate of the casing.
 7. A tool for repairing leaks in casing, comprising: a drill for boring through the casing; a seal for sealing around a hole in the casing; and a supply of sealing fluid.
 8. The tool of claim 7, wherein the supply of sealing fluid comprises cement stored in a chamber within the tool.
 9. The tool of claim 7, wherein the supply of sealing fluid comprises a reservoir of sealing fluid at a surface location connected to the tool by coiled tubing.
 10. The tool of claim 7, wherein the seal is a set of packers capable of setting above and below the hole in the casing. 